The present invention relates generally to liquid crystal displays, and more particularly, to a method of and an adhesive for attaching optical components and optical component assemblies to a liquid crystal display.
Liquid crystal displays (LCDs) include a liquid crystal material sandwiched between two sheets of glass. The two sheets of glass are typically a substrate and a filter. Frequently, it is desirable to alter or enhance the performance of the LCD by attaching additional optical components to one or both of the LCD's two sheets of glass. These additional optical components can be items such as glass plates, diffusers, rigid compensators, heaters, and flexible films such as polarizers, retarders and dry film adhesives. Also, two or more of these optical components can be pre-assembled into an optical component assembly which is subsequently attached to the LCD. This pre-assembly approach is detailed in co-pending and commonly assigned U.S. patent application File No. 94CR088 filed on even date herewith and which is herein incorporated by reference.
Attaching additional optical components or optical component assemblies to an LCD presents a number of significant problems. First, the choice of adhesive used is critical to the display's performance. For instance, the index of refraction of the adhesive should closely match that of the optical components. Also, the adhesive should be as transparent as possible. These limitations and others render many adhesives undesirable choices.
A second problem is related to the sensitivity of LCDs to strain. Strain on an LCD can cause performance defects such as Newton rings. High durometer (hard) adhesives, such as epoxy, used to attach optical components to an LCD typically cause strain on the LCD, and thus cause strain related defects as well. A related problem is due to the expensive nature and repairability of large LCDs. Once laminated (i.e., once the optical components or assemblies have been attached to the LCD), the LCD is generally not considered repairable. This is largely due to the strength of the bond between the LCD glass and the glass of the optical component resulting from the adhesive. Because of the adhesives used in the prior art, disassembly is generally not possible without damaging the display.
Some manufacturers of LCDs have, as a result of the problems associated with the use of available adhesives and known assembly methods, turned away from the adhesive approach to attaching optical components to the LCD. Instead, they mechanically attach the component to the LCD such that an air gap is formed between the two, thereby reducing strain and possibly improving repairability. However, this method is undesirable because it adversely effects the reflectance and contrast of the display. Consequently, there is a need for an assembly process and adhesive which eliminate the problems identified above and provides high yields and repairable LCD stack-ups.